1. Technical Field
This invention generally relates to podiums, and in particular, it relates to a motor-driven, adjustable height podium having a relay circuit for controlling the motor which is configured to avoid a short-circuit condition in the event relays should stick shut.
2. Background
The podium serves a variety of functions for a speaker. Among these are supporting the speaker's reading material, providing a leaning surface for the speaker, and providing a security barrier between the speaker and his audience. Podiums are used in a variety of speaking settings from business to entertainment to religious ceremonies, being known in the latter as pulpits. While speakers come in all different sizes, a given podium is typically limited to a fixed height. Height incompatibility between the speaker and podium can make it difficult and uncomfortable for the speaker to read from, or to lean on, the podium. For example, a speaker who is too tall for the podium will have to hunch over to use the podium, while a speaker who is too short will have to strain upwards and may even be substantially eclipsed by a high podium. This problem is exacerbated in the case of children who may be completely precluded from using a podium without auxiliary height adjusters, such as stairs, boxes, etc.
Podiums have been developed which contain built-in height adjustment features. One example is Richardson, U.S. Pat. No. 3,936,109, which teaches a portable podium having a pedestal consisting of a plurality of threaded pipe sections interconnected by threaded couplings. By varying the number of pipe sections employed, the pedestal links and hence the height of the podium, may be adjusted to an extent. Also known in the art are powered adjustable height podiums which typically use an electric motor to provide the motive force for raising and lowering, and thereby adjusting the height of the podium to suit the speaker. Motor control circuitry comprising up and down relays is typically utilized to send current through the motor windings as appropriate for raising or lowering the podium.
Prior art FIG. 1 shows an example of typical prior art podium motor control relay circuitry showing the relays open (de-energized). A common problem with such circuitry is the occurrence of a short circuit condition in situations when both the up and down relays were shut, or energized, at the same time. An example of how such a situation could occur is provided by that of children playing on a prior art motorized adjustable height podium. If a child should sit on the height adjustable part of the podium, and move the podium control switch to up, thus shutting the up relays in the motor control circuitry, the motor windings would draw an unusually large current, the system being designed to move the weight of papers and the like, rather than the multiple pounds of a child. Depending on the weight of the child, the size of the current drawn might be sufficient to fuse the up relays shut. Then, when the down direction was selected on the control switch, thus shutting the down relays in the motor control circuitry, a short circuit condition was created between the hot and neutral power leads; for example through points A, B, C, D, E, F and G in FIG. 1. The result was electrical destruction of the relays and other control circuit components. Furthermore, because these prior art motor control circuits were configured on printed circuit boards, replacement of one damaged component necessitated replacement of the entire printed circuit board into which that component was integrated.
Accordingly, it is an object of the present invention to provide a motor-driven, adjustable height podium with motor control circuitry in which a short circuit is avoided in the event that both up and down relays should be shut at the same time.
It is another object of the present invention to provide a motor driven, adjustable-height podium with motor control circuitry which utilizes individual components connected together by standard copper wires, rather than printed circuit boards, so that the components, such as relays, are easily replaceable when damaged.